There is no such component within kerberos environment. Kerberos uses only symmetric encryption and does not make use of any public key component.
The other answers are incorrect because :
Symmetric key cryptography is a part of Kerberos as the KDC holds all the users’ and services’ secret keys. Authentication service (AS) : KDC (Key Distribution Center) provides an authentication service
Principals : Key Distribution Center provides services to principals , which can be users , applications or network services. References: Shon Harris , AIO v3 , Chapter -4: Access Control , Pages : 152-155.